just count lines as a machine would, then... ;)

I normally count

def func(x):
return whatever

as one line, so by that metric this one is 0

That's one line tho.

First 0-line solution I've seen

I am fully aware that this sucks

The reversal is memory-intensive for large arrays, I could have used next() syntax to achieve the same thing with the reversal generator.

Also, I forgot about .append()

turning string.upper() into a list is redundant - you can get the same result by just doing len(string).

Disappointing lack of pigeonhole principle in the solutions I've seen. You want to make a set out of a million-character string?